It is known in the prior art to generate pulse width modulated control signals for an inverter coupled with a load, such as an AC induction motor, to provide a synthesized AC sine wave voltage output to that load, as set forth at pages 15-39 to 15-42 of the Electronic Engineers Handbook published in 1975 by McGraw-Hill Book Company. It is known to vary the DC input voltage and the pulse width control for determining the output voltage applied to the load.
It is known to generate a synthesized sine wave of voltage output for energizing one phase of a three-phase AC motor and providing suitable 120 degree phase shifting of that output for energizing the other phase of the motor, as described in U.S. Pat. No. 4,099,109 of A. Abbondanti.
The optimum voltage wave form to energize an AC motor is a sine wave. At the present time it is not practical to provide a linear amplifier to develop the power level required by many AC motors, a switching mode can be employed to provide the desired voltage control and power level for the AC motor load. A sine wave form is chopped by a sawtooth or triangular carrier wave that determines the output voltage wave form applied to the converter coupled with the motor. The motor is energized with a voltage that is synthesized from a pulse width modulated series of pulses.